The broad objective of this proposal will be to continue the ongoing studies to map protein protein interactions of Pit1. This study will begin to assess how cell signaling influences such interactions and, specifically, it is proposed to assess how an Ets repressor protein ERF negatively regulates prolactin gene regulation. First, the applicant proposes to identify the endogenous ERF protein and characterize its subcellular localization during critical periods within the cell cycle and in response to activation of signal transduction cascades. Second, the requirements for Pit-1 nuclear localization will be precisely identified so as to permit further protein protein analysis by FRET microscopy. Continuing on this theme, the final aim will investigate the association of Pit-1 and its protein partners with the nuclear matrix.